The long-range project concerning the structure and behavior of the human X chromosome will be continued along two lines. Abnormal X chromosomes will be studied as they are found in patients, usually ascertained for primary amenorrhea. For the study on the correlation between the type of X chromosome abnormalities and the phenotype in Turner's syndrome over 800 cases have been collected and 200 more will be obtained from Dr. Paul E. Polani (London, England). Our first attempt will be to correlate the length of the Xq deletions and the symptoms caused by them. The study of Bloom's syndrome will be continued in a "blind study" on the chromosomes of the heterozygotes and suitable controls. Crossing-over in diplochromosomes will be analyzed as a sequel to our study on mitotic crossing-over. The behavior of inactive centromeres in human chromosomes is under study in an idic(Xp-) chromosomes, in a translocation chromosome between no.6 and 19, and in the X chromosomes of two phenotypically normal women. The application of observations on mitotic aberrations in malignant cells to cancer diagnosis will be continued. A comprehensive material will be collected at the Women's Clinic, University of Helsinki. After the material has been analyzed cytogenetically, the findings will be correlated with the diagnosis and various other parameters. BIBLIOGRAPHIC REFERENCE: Daly, R.F., K. Patau, E. Therman, and G.E. Sarto. Structure and Barr body formation of an Xp+ chromosome with two inactivation centers. Am. J. Hum. Genet. 29:83-93, 1977.